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What you should know about the Hidden Protected Area on IBM ThinkPad drives

On most ThinkPad hard drives is a segment called the Hidden Protected Area (HPA), which contains recovery data. Using disk imaging tools on a ThinkPad with a HPA can have unexpected consequences.

IBM has long been shipping many of its ThinkPad laptops with something called the Hidden Protected Area (HPA) on...

each machine's hard drive. The HPA is worth discussing, because little is known about it outside of IBM's technical documents, or the effects it can have on the way the system works -- especially when using utilities that deal with the hard drive on a low level.

The HPA is a segment located at the end of the hard disk (which is preinstalled on many ThinkPad machines). It is typically hidden from the rest of the system and contains data needed to recover the ThinkPad to its factory-installed state. Each HPA can be subdivided into one or more Protected Service Areas (PSAs). In a sense, these are to the HPA what logical partitions are to a physical partition. For instance, the ThinkPad T41 has eight PSAs in its HPA, each with its own utilities and disk images (for emergency recovery).

What's important about the HPA is how it is concealed from the system at large. It is managed through the ThinkPad's BIOS, which can set the HPA to one of three modes: secure, normal or disabled. When the HPA is set to "secure," the BIOS tricks the host system into thinking that the area on the hard disk occupied by the HPA is simply not available. (This is done by providing slightly different partition table information than what's actually written on the disk, so even an OS-level application will not be able to read the HPA. Essentially, it's concealed in hardware.

If you're using disk imaging tools on a ThinkPad with an HPA, this can have some unexpected consequences. If an HPA has not been unprotected through BIOS, disk-cloning functions will fail because of the way the BIOS deliberately reports incorrect disk geometry for the source drive. So if you're attempting to clone a ThinkPad drive that has an HPA, be sure to boot into the BIOS (usually by pressing Enter or the Access IBM button at boot time) and set the HPA (described as the "IBM Predesktop Area" in the BIOS) to "Disabled." This will cause the system to report the drive's geometry accurately until reset.

Note: With the May 2005 sale of IBM's personal computing division, including the ThinkPad line, to computer maker Lenovo in China, it's not clear if future iterations of the ThinkPad will have the HPA. However, my guess is they will, and, in any event, there are enough existing ThinkPad models with the HPA that this is worthy of note.

Serdar Yegulalp is editor of the Windows Power Users Newsletter. Check it out for the latest advice and musings on the world of Windows network administrators -- and please share your thoughts as well!

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This was last published in March 2006

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